Thursday, October 29, 2009
GREAT MIGRATION
THE earth thunders with the sound of a million pounding hooves. The mass of heaving bodies surges forward, kicking up a billowing cloud of red dust. The animals gallop on spindly legs as the herd moves past rolling valleys and hills, crosses open grasslands, and traverses rivers and streams. They advance in a great wave, leaving behind huge swaths of grass cropped down to the roots. This vast herd of bellowing, stampeding creatures makes up one of the greatest natural wildlife spectacles on earth—the great migration of wildebeests.
An estimated 1.5 million wildebeests roam the Serengeti. This is an odd-looking creature, with a long head and glossy eyes, which are located far apart and high up on the skull. Its cowlike horns curve slightly downward and outward and then hook upward. Its back slopes down toward hindquarters that appear weak and out of proportion to the animal's strong shoulders and neck. Thin, spindly legs support the weight of the wildebeest's heavy body. With a long whitish beard under the chin, a dark mane on the neck, and a tail like that of a horse, the wildebeest resembles a combination of several different animals.
The antics of wildebeests are often clownish and entertaining. When gathered in large herds, they produce a noisy bellowing sound that resembles a chorus of thousands of frogs. Standing on the open plains, they seem to wear a bewildered, surprised look as they stare out at the world around them.
At times, a wildebeest bull will race across the plains, prancing sideways and running in circles. Tossing his head, he bucks and bounces on stiff legs, kicking up dust in a comical manner. Some say that these actions are intended to impress females or to warn other males with a show of prowess. Sometimes, though, the bull just appears to be feeling frisky.
Born Into a Hostile World
When the time is right, the wildebeests begin giving birth. They have the unique ability to synchronize the birth of their young, dropping 80 to 90 percent of their calves within a three-week period. During this time the herd swells with thousands of bleating baby wildebeests. Each mother must quickly bond with her calf, for if the herd stampedes, the mother and her calf could easily become separated, and the calf would have little chance of survival on its own.
The young are born into a hostile world of ever-watchful predators. Females wait until there are no signs of danger before giving birth. However, if surprised by a predator, they have the incredible ability to interrupt the birth process and run away. Then, at a later time when no danger threatens, they are able to complete the birth of their calf.
The calf itself seems to have an inborn sense of danger and is on its feet within a few minutes of birth. After a week, the youngster will be able to gallop across the plains at 30 miles [50 km] per hour.
A Time to Move
Wildebeests migrate in great herds across the Serengeti. The key to their mass movement is the rain. The rainfall is governed by weather patterns that move in annual cycles. Throughout the year it is usually raining somewhere within the bounds of this vast grassland.
Wildebeests need water daily and must have a constant supply of grass to feed on. As long as food and water are available, they stay put. But as the dry season progresses, the grass on the plains begins to dry up and water sources disappear. The herds of wildebeests cannot wait for the rains to come to them. They must follow the rain.
Wherever the rain falls, the dry plains are quickly transformed. Within a few days, green sprouts push up through the soil and produce a green flush of grass. These tender blades are full of nutrition and moisture—a powerful attraction for wildebeests.
These creatures have an ability to detect rainfall, even at great distances. No one is sure how they know that it is raining in another part of the Serengeti—whether it is by seeing the billowing thunderheads towering in the distance or by smelling the moisture in the dry air. At any rate, to survive, the herds must move. And move they do!
A Perilous Journey
Herds must cross swift-flowing rivers
In the beginning the departure is gradual. Wildebeests are gregarious creatures; when one animal starts to walk in a certain direction, others around it stop grazing and try to follow. Soon the whole herd is surging forward in a dramatic exodus. Pushed by thirst and hunger, they move onward. Sometimes they run. At other times they plod along in drawn-out lines, creating deep ruts in the dusty soil.
Their journey is fraught with danger. Predators follow the immense herds of ungulates, keeping a keen eye on any animal that is slow-footed, lame, or sick. As the wildebeests advance, they enter the territories of lion prides, which wait in ambush. Hiding in the long grass, the big cats rush into the mass of grazing animals, causing them to scatter in panic. Leopards, cheetahs, wild dogs, and hyenas all take advantage of any animals that fall behind or drift away from the main herd. When a kill is made, vultures appear. Squabbling and fighting over the remains, they leave nothing behind but a frame of bones, which bleach white in the hot African sun.
Swift-flowing rivers create formidable barriers that the herd must cross. River crossings are spectacular events, with thousands of animals plunging from high banks into the water below. Most make it safely to the opposite side. Others are carried away by the current or are taken by the crocodiles that wait just below the surface of the water. This perilous journey is undertaken yearly. When completed, it may cover a distance of some 2,000 miles [3,000 km].
Man—The Greatest Predator
For thousands of years, man had little impact on the migration of the wildebeests. Now man poses the biggest threat to this spectacle. In recent decades the governments of Tanzania and Kenya have endeavored to protect the animals of the Serengeti. Yet, even though the wildebeest migration takes place largely within the protected borders of wildlife sanctuaries, thousands of the animals are illegally trapped and killed by poachers. Armed with wire snares, poison arrows, and guns, they hunt animals to supply game meat and trophies to eager buyers. An army of game wardens and rangers patrol the protected areas, but the Serengeti is so large that it is almost impossible to protect it fully. As human populations grow, the pressure to encroach on these fertile grasslands increases. The setting aside of large tracts of land for wildlife is a bitter issue that is constantly debated.
At one time millions of bison roamed the plains of North America. Now they are gone. Some fear that the same fate awaits the last great herds of wildebeests in East Africa. It would be a sad day if we were to witness the disappearance of such an awesome natural wonder.
MYSTERY OF TOUR GENE
Take a good, long look at yourself in the mirror. Note the color of your eyes, the texture of your hair, the shade of your complexion, and the shape of your body. Think about the talents that you possess. Why do you look the way you do? Why do you have the particular traits and talents that you do? Today the mystery is being clarified through an understanding of genetics—the study of heredity—and the effects of environment.
'Genetics?' you moan. 'That subject sounds too scientific and too difficult to understand!' However, have you ever told someone that she has her father's green eyes but her mother's red hair and freckles? If so, you already know a basic fact of genetics—physical traits are passed from parent to child. In addition, that fact may be the decisive start to your understanding how man got here—by evolution or by creation. To begin, let us see how each of us carries the heritage of many generations.
Your body is made up of tiny living units called cells—some 100 trillion of them, according to one estimate. Inside each cell, within its nucleus, there are thousands of genes. They are individual units of heredity that control the cell and therefore determine some of your characteristics. Many genes may order your blood type; others, your hair texture, your eye color, and so on. So each cell carries a miniature blueprint or codebook made up of genes, which contains all the instructions needed to build, repair, and run your body.) Could all of this have happened by accident?
How the Mystery Was UnraveledThe theory that traits were inherited through the blood was devised by Aristotle in the fourth century B.C.E. and was generally accepted for over a thousand years. This so affected the thinking of the day that in the English language, people speak of bloodlines and blood relatives.
In the 17th century, egg cells and sperm cells were discovered, but their actual role was misunderstood. Some thought that tiny, fully formed creatures were present in either the egg or the sperm. By the 18th century, though, researchers correctly recognized that an egg and a sperm combine to form an embryo. Nevertheless, an accurate explanation of heredity was still to come.
It wasn't until 1866 that an Austrian monk named Gregor Mendel published the first correct theory of heredity. From his experiments with garden peas, Mendel discovered what he called "discrete hereditary elements" hidden in sex cells, and he asserted that these were responsible for the passing on of traits. These "discrete hereditary elements" we now call genes.
About the year 1910, genes were found to be located on cell structures called chromosomes. Chromosomes consist primarily of protein and DNA (deoxyribonucleic acid). Since scientists were already aware of the important role of proteins in other cell functions, they assumed for many years that chromosomal proteins carry genetic information. Then, in 1944, researchers presented the first proof that genes consist of DNA, not protein.
In 1953, when James Watson and Francis Crick discovered the chemical structure of DNA, coiled threadlike molecules, man's unraveling of the mystery of life took a great step forward. Read the next article to learn what science discovered
'Genetics?' you moan. 'That subject sounds too scientific and too difficult to understand!' However, have you ever told someone that she has her father's green eyes but her mother's red hair and freckles? If so, you already know a basic fact of genetics—physical traits are passed from parent to child. In addition, that fact may be the decisive start to your understanding how man got here—by evolution or by creation. To begin, let us see how each of us carries the heritage of many generations.
Your body is made up of tiny living units called cells—some 100 trillion of them, according to one estimate. Inside each cell, within its nucleus, there are thousands of genes. They are individual units of heredity that control the cell and therefore determine some of your characteristics. Many genes may order your blood type; others, your hair texture, your eye color, and so on. So each cell carries a miniature blueprint or codebook made up of genes, which contains all the instructions needed to build, repair, and run your body.) Could all of this have happened by accident?
How the Mystery Was UnraveledThe theory that traits were inherited through the blood was devised by Aristotle in the fourth century B.C.E. and was generally accepted for over a thousand years. This so affected the thinking of the day that in the English language, people speak of bloodlines and blood relatives.
In the 17th century, egg cells and sperm cells were discovered, but their actual role was misunderstood. Some thought that tiny, fully formed creatures were present in either the egg or the sperm. By the 18th century, though, researchers correctly recognized that an egg and a sperm combine to form an embryo. Nevertheless, an accurate explanation of heredity was still to come.
It wasn't until 1866 that an Austrian monk named Gregor Mendel published the first correct theory of heredity. From his experiments with garden peas, Mendel discovered what he called "discrete hereditary elements" hidden in sex cells, and he asserted that these were responsible for the passing on of traits. These "discrete hereditary elements" we now call genes.
About the year 1910, genes were found to be located on cell structures called chromosomes. Chromosomes consist primarily of protein and DNA (deoxyribonucleic acid). Since scientists were already aware of the important role of proteins in other cell functions, they assumed for many years that chromosomal proteins carry genetic information. Then, in 1944, researchers presented the first proof that genes consist of DNA, not protein.
In 1953, when James Watson and Francis Crick discovered the chemical structure of DNA, coiled threadlike molecules, man's unraveling of the mystery of life took a great step forward. Read the next article to learn what science discovered
GLOBAL WARMING
Many believe that human activities are a major cause of global warming, which may have catastrophic consequences for the climate and the environment. For example, large-scale melting of land-based ice and the expansion of the oceans as water warms could cause sea levels to rise drastically. Low-lying islands such as Tuvalu could disappear, as could large parts of the Netherlands and Florida, to name just two other areas. Millions of people could be displaced from such places as Shanghai and Calcutta, as well as parts of Bangladesh.
At the same time, rising temperatures could intensify storms, floods, and droughts. In the Himalayas, disappearing glaciers—from areas that feed seven river systems—could cause shortages of freshwater for 40 percent of the world’s population. Also at risk are thousands of species of animals, including polar bears, whose hunting grounds are largely on the ice. Indeed, reports already indicate that many bears are losing weight and some are even starving.
Rising temperatures may also foster the spread of disease by enabling mosquitoes, ticks, and other disease-carrying organisms, including fungi, to spread farther afield. “The dangers posed by climate change are nearly as dire as those posed by nuclear weapons,” says the Bulletin of the Atomic Scientists. “The effects may be less dramatic in the short term . . . , but over the next three to four decades climate change could cause irremediable harm to the habitats upon which human societies depend for survival.” Adding an even more ominous note, some scientists believe that changes attributed to global warming are occurring faster than they had expected
At the same time, rising temperatures could intensify storms, floods, and droughts. In the Himalayas, disappearing glaciers—from areas that feed seven river systems—could cause shortages of freshwater for 40 percent of the world’s population. Also at risk are thousands of species of animals, including polar bears, whose hunting grounds are largely on the ice. Indeed, reports already indicate that many bears are losing weight and some are even starving.
Rising temperatures may also foster the spread of disease by enabling mosquitoes, ticks, and other disease-carrying organisms, including fungi, to spread farther afield. “The dangers posed by climate change are nearly as dire as those posed by nuclear weapons,” says the Bulletin of the Atomic Scientists. “The effects may be less dramatic in the short term . . . , but over the next three to four decades climate change could cause irremediable harm to the habitats upon which human societies depend for survival.” Adding an even more ominous note, some scientists believe that changes attributed to global warming are occurring faster than they had expected
WATER AND YOU
According to a saying, “if you run out of water, you run out of life.” Some experts would say that those words seem more prophetic than proverbial. Each year about two million people die as a result of poor sanitation and contaminated water, and 90 percent of the victims are children.
HOW do you get water? Do you just turn on a faucet and out it pours? Or, as is common in some lands, do you have to walk a long distance, wait in line, and then carry a heavy bucket of the precious liquid back to your home? Does it take you several hours each day just to get enough water for washing and cooking? In many lands, water is that scarce and that difficult to obtain! In her book Water Wars—Drought, Flood, Folly, and the Politics of Thirst, Diane Raines Ward notes that 40 percent of the world’s population “carry their water from wells, rivers, ponds, or puddles outside of their homes.” In some countries, women may spend up to six hours fetching water for their families, lugging it home in containers that, when full, weigh more than 40 pounds.
WATER UNDER THREAT
“The Aral Sea in Central Asia was the fourth-largest lake on the planet in 1960. By 2007 it had shrunk to 10 percent of its original size.”—Scientific American.
The five Great Lakes of the United States and Canada—Lakes Erie, Huron, Michigan, Ontario, and Superior—are shrinking “at an alarming pace.”—The Globe and Mail.
At one time, Australia’s Deniliquin mill processed enough grain to meet the needs of 20 million people. Now, however, the rice crop has been reduced by 98 percent, and the mill closed in December 2007. The cause? “Six long years of drought.”—The New York Times.
The fact is that over a third of the world’s population is seriously affected by a water and sanitation crisis. The problem is particularly severe in Africa, where 6 out of 10 people do not even have a proper toilet—a factor that, according to a World Health Organization report, contributes to “the transfer of bacteria, viruses and parasites found in human excreta which . . . contaminate water resources, soil and food.” Such contamination, the report notes, “is a major cause of diarrhoea, the second biggest killer of children in developing countries, and leads to other major diseases such as cholera, schistosomiasis, and trachoma.”
Water has been called liquid gold, the oil of the 21st century. Yet, nations are squandering the precious commodity to such a degree that their principal rivers have hardly anything left to pour into the sea. As irrigation and evaporation take their toll, prominent rivers are drying up, including the Colorado River in the western United States, the Yangtze in China, the Indus in Pakistan, the Ganges in India, and the Nile in Egypt. What is the ultimate solution?.
HOW do you get water? Do you just turn on a faucet and out it pours? Or, as is common in some lands, do you have to walk a long distance, wait in line, and then carry a heavy bucket of the precious liquid back to your home? Does it take you several hours each day just to get enough water for washing and cooking? In many lands, water is that scarce and that difficult to obtain! In her book Water Wars—Drought, Flood, Folly, and the Politics of Thirst, Diane Raines Ward notes that 40 percent of the world’s population “carry their water from wells, rivers, ponds, or puddles outside of their homes.” In some countries, women may spend up to six hours fetching water for their families, lugging it home in containers that, when full, weigh more than 40 pounds.
WATER UNDER THREAT
“The Aral Sea in Central Asia was the fourth-largest lake on the planet in 1960. By 2007 it had shrunk to 10 percent of its original size.”—Scientific American.
The five Great Lakes of the United States and Canada—Lakes Erie, Huron, Michigan, Ontario, and Superior—are shrinking “at an alarming pace.”—The Globe and Mail.
At one time, Australia’s Deniliquin mill processed enough grain to meet the needs of 20 million people. Now, however, the rice crop has been reduced by 98 percent, and the mill closed in December 2007. The cause? “Six long years of drought.”—The New York Times.
The fact is that over a third of the world’s population is seriously affected by a water and sanitation crisis. The problem is particularly severe in Africa, where 6 out of 10 people do not even have a proper toilet—a factor that, according to a World Health Organization report, contributes to “the transfer of bacteria, viruses and parasites found in human excreta which . . . contaminate water resources, soil and food.” Such contamination, the report notes, “is a major cause of diarrhoea, the second biggest killer of children in developing countries, and leads to other major diseases such as cholera, schistosomiasis, and trachoma.”
Water has been called liquid gold, the oil of the 21st century. Yet, nations are squandering the precious commodity to such a degree that their principal rivers have hardly anything left to pour into the sea. As irrigation and evaporation take their toll, prominent rivers are drying up, including the Colorado River in the western United States, the Yangtze in China, the Indus in Pakistan, the Ganges in India, and the Nile in Egypt. What is the ultimate solution?.
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